Led and method of manufacturing the same

ABSTRACT

An LED can include a pair of electrode members, and an LED chip joined to a chip mount portion disposed at the extremity of one of the pair of electrode members. The LED chip can be electrically connected to the pair of electrode members. A transparent resin portion can include a wavelength conversion material mixed therein, the transparent resin portion formed in such a manner as to surround the LED chip, wherein the LED chip is positioned offset toward one side in the transparent resin portion, and wherein the wavelength conversion material mixed in the transparent resin portion has a higher density around the LED chip within the transparent resin portion.

This application is a divisional application claiming priority under 35U.S.C. §120 to co-pending and commonly assigned U.S. patent applicationSer. No. 11/199,168, filed on Aug. 9, 2005, which claims priority under35 U.S.C. §119 to Japanese Patent Application No. 2004-231828 filed onAug. 9, 2004, both of which are hereby incorporated in their entirety byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an LED adapted to allow light from anLED chip and excitation light from a fluorescent material to be emittedas color mixture light.

2. Description of the Related Art

A white LED is hitherto known that converts, through its transparentresin portion, blue light emitted from a blue LED chip into yellow lightfor mixture with the blue light to externally emit a resultant whitelight.

Such a white LED is configured as shown in FIG. 3, for example.Referring to FIG. 3, the white LED 1 includes a chip substrate 2, a blueLED chip 3 mounted on the chip substrate 2, and a transparent resinportion 4 having a fluorescent material 4 a mixed therein. Thetransparent resin portion 4 is formed on top of the chip substrate 2 insuch a manner as to surround the blue LED chip 3.

The chip substrate 2 is formed from a heat-resistant resin, such as aflat copper-clad wiring board for example, and includes on its surfacesa chip mount land 2 a, a connection land 2 b, and surface mountingterminals 2 c and 2 d extending therefrom via opposite end edges to itsundersurfaces. The blue LED chip 3 is joined via e.g., die bonding, ontothe chip mount land 2 a of the chip substrate 2. An electrode on top ofthe blue LED chip 3 is electrically connected via wire bonding to theadjoining connection land 2 b. The blue LED chip 3 is formed as a GaNchip, for example, such that it emits light having a peak wavelength at450 to 470 nm, for example, when a drive voltage is applied.

The transparent resin portion 4 is formed from, e.g., transparent epoxyresin with the fluorescent material 4 a in the form of fine particlesmixed therein, and is molded onto the chip substrate 2 before hardening.During operation, blue light from the blue LED chip 3 impinges on thetransparent resin portion 4 so that the fluorescent material 4 a isexcited to generate yellow light as excitation light from thefluorescent material 4 a, thus emitting white light as a result ofmixture of the different colors of light.

The fluorescent material 4 a is, for example, a fluorescent materialissuing a wide range of colored lights around true yellow. Thefluorescent material is a material such as cerium-doped YAG fluorescentmaterial, cerium-doped TAG fluorescent material, or orthosilicatefluorescent material (BaSrCa)SiO4. The fluorescent material 4 a beingarranged to issue a fluorescent light having its peak wavelength at 530to 590 nm, for example.

According to the thus configured white LED 1, application of the drivevoltage to the blue LED chip 3 via the surface mounting terminals 2 cand 2 d allows emission of light from the blue LED chip 3. The resultantblue light impinges on the fluorescent material 4 a mixed in thetransparent resin portion 4 to thereby excite the fluorescent material 4a to generate yellow light. This yellow light mixes with the blue lightfrom the blue LED chip 3, resulting in white light issued to theexterior.

However, as size-reduction requirements progress in the thus configuredwhite LED 1, there arises a need to secure the space for a bonding wirefrom the blue LED chip 3 to the connection land 2 b, making it difficultto position the blue LED chip 3 at or near the center of the chipsubstrate 2 or near the center of the transparent resin.

As shown in FIG. 3, this leads to a comparatively elongated distance bywhich the blue light L1 issued from the blue LED chip 3 toward theconnection land 2 b travels through the interior of the transparentresin portion 4. Consequently, more fluorescent material 4 a is excitedby the blue light L1 from the blue LED chip 3, allowing the lightexternally emitted from the transparent resin portion 4 in the directionof the blue light L1 to contain more yellow light which can result in ayellowish white light.

Furthermore, since the transparent resin portion 4 is made, for example,by molding and then hardening epoxy resin with the fluorescent material4 a mixed therein, the fluorescent material 4 a tends to settle onto theunderlying chip substrate 2 before the hardening, as shown in FIG. 4.This characteristic is due to gravity, and based on the difference inthe specific gravity between the fluorescent material 4 a and the epoxyresin.

For this reason, light L2 outgoing laterally from the sidewalls of theblue LED chip 3 travels through part of the transparent resin portion 4containing less fluorescent material 4 a. This results in lessfluorescent material 4 a being excited by the blue light L2 from theblue LED chip 3, whereupon the outgoing light from the transparent resinportion 4 to the exterior in the direction of the blue light L2 containsless yellow light which can result in white light that is short ofyellow tint (having a blue tint).

This means that different colors of light appear depending on theviewing direction in such a type of LED.

SUMMARY OF THE INVENTION

The present invention was conceived in view of the above and otherproblems and deficiencies. An aspect of the present invention is toprovide an LED with a simple configuration, adapted to emit light of auniform color in its entirety even if the LED chip is not positioned ator near the center of the chip substrate.

According to another aspect of the invention there is provided an LEDthat can include a pair of electrode members, an LED chip joined to achip mount portion disposed at the extremity of one of the pair ofelectrode members, the LED chip electrically connected to the pair ofelectrode members, and a transparent resin portion with wavelengthconversion material mixed therein. The transparent resin portion can beformed in such a manner as to surround the LED chip, wherein the LEDchip is positioned offset toward one side in the transparent resinportion, and wherein the wavelength conversion material mixed in thetransparent resin portion has a higher density around the LED chipwithin the transparent resin portion.

An LED made in accordance with the principles of the invention caninclude a lens portion made of a transparent resin surrounding the LEDchip and the transparent resin portion, wherein the pair of electrodemembers are two lead frames extending in parallel with each other.

The pair of electrode members can be formed on a chip substrate and canbe in the form of electrically conductive patterns extending to theunderside of the chip substrate to define surface mounting terminals.The transparent resin portion can be filled within a recessed portionthat is upwardly flared so as to allow exposure of the chip mountportion in the form of a frame-shaped member formed on the chipsubstrate. When formed, the transparent resin portion can be hardenedkeeping the transparent resin portion such that the side thereof closerto the LED chip orients downward.

According to another aspect of the invention there is provided a methodof manufacturing an LED that can include joining an LED chip onto a chipmount portion disposed at the extremity of one of a pair of electrodemembers and electrically connecting the LED chip to the pair ofelectrode members. The method can also include forming a transparentresin portion with wavelength conversion material mixed therein in sucha manner as to surround the LED chip, wherein the LED chip is positionedoffset toward one side in the transparent resin portion, and when thetransparent resin portion is hardened, keeping the transparent resinportion such that the side thereof closer to the LED chip orientsdownward.

The LED chip can emit light when a drive voltage is applied to the LEDchip via the pair of electrode members. Light emitted from the LED chipthen issues to the exterior through the transparent resin portion. Atthat time, the light emitted from the LED chip impinges on thewavelength conversion material within the transparent resin portion toexcite the wavelength conversion material to issue excitation light.Color mixture light thus issues forth toward the exterior as a result ofa mixture of colors of the light from the LED chip and the excitationlight from the wavelength conversion material.

At that time, the LED chip may be offset toward one side within thetransparent resin portion, and hence light emitted from the LED chiptoward the other sides travel through longer distances within thetransparent resin portion. However, in the regions outside thesurrounding regions of the LED chip within the transparent resinportion, the density of the wavelength conversion material may be lowsuch that there is not much difference between the number of wavelengthconversion particles struck by light emitted from the LED chip towardone side and the number of wavelength conversion particles struck bylight emitted toward other sides.

Accordingly, light emitted from the entire transparent resin portion ofthe LED to the exterior is prevented from causing unevenness in colordepending on direction, ensuring emission of light of generally uniformcolor. In this case, by merely controlling the distribution of densityof the wavelength conversion material mixed in the transparent resinportion, the present LED can be fabricated at low cost without usingadditional or unnecessary members, etc., and without the need toincrease the number of production steps.

A cannonball-type LED may be configured in a case where the pair ofelectrode members are two lead frames extending in parallel with eachother and where the LED is provided with a lens portion made oftransparent resin surrounding the LED chip and the transparent resinportion.

A surface-mount-type LED may be configured in a case where the pair ofelectrode members are formed on the chip substrate and are made ofelectrically conductive patterns extending to the underside of the chipsubstrate to define the surface mounting terminals.

A surface-mount-type LED provided with a so-called lamphouse can beadapted to reduce the outgoing light upward in a case where thetransparent resin portion is filled within the recessed portion that isupwardly flared so as to allow exposure of the chip mount portion in theform of a frame-shaped member formed on the chip substrate.

In a case where the transparent resin portion, when formed, is hardenedin such a manner that the side closer to the LED chip of the transparentresin portion is oriented downward, the wavelength conversion materialmixed in the pre-hardening transparent resin portion can settle down dueto gravity based on the difference in the specific gravity between thewavelength conversion material and the transparent resin. Thus, thewavelength conversion material can gather toward the LED chip near thelower end of the transparent resin portion. As a result, when thetransparent resin portion is hardened, the wavelength conversionmaterial gathers around the LED chip within the transparent resinportion to present a higher density. Thus, the present LED can easily befabricated at low cost without the need for additional members and/oradditional process steps, by orienting the side of the transparent resinportion that is closer to the LED chip downward when the transparentresin portion is hardened.

The transparent resin portion, when hardened, can be kept such that theside closer to the LED chip of the transparent resin portion orientsdownward, whereby the wavelength conversion material mixed in thepre-hardening transparent resin portion settles downward due to gravityand based on the difference in the specific gravity between thewavelength conversion material and the transparent resin. Thus, thewavelength conversion material can gather toward the side closer to theLED chip of the transparent resin portion. As a result, when thetransparent resin portion hardens, the wavelength conversion materialgathers around the LED chip within the transparent resin portion topresent a high density.

In consequence, light emitted from the LED chip toward the other sidestravels through longer distances within the transparent resin portion.However, since the density of the wavelength conversion material withinthe transparent resin portion is low in the regions outside thesurrounding regions of the LED chip within the transparent resinportion, there is not much difference between the number of wavelengthconversion particles struck within the transparent resin portion by thelight issuing from the LED chip toward one side and the number ofwavelength conversion particles stuck by the light issuing toward theother sides.

Accordingly, light emitted from the entire LED transparent resin portionto the exterior does not exhibit unevenness in color depending ondirection, ensuring emission of light of generally uniform color.

In this case, the present LED can be fabricated at low cost withoutusing any specific members, etc., and without increasing the number ofproduction steps, by controlling the distribution of density of thewavelength conversion material mixed in the transparent resin portion.This can be accomplished by keeping the transparent resin portion suchthat the side thereof closer to the LED chip orients downward duringproduction.

In this manner, an LED can be provided that is adapted to issue light ofgenerally uniform color through a simple configuration even when the LEDchip is not located at or near the center of the chip substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, aspects, features and advantages of theinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic sectional view showing the configuration of anembodiment of an LED made in accordance with the principles to theinvention;

FIG. 2 is a schematic sectional view showing hardening of a transparentresin portion in accordance with a manufacturing process for the LED ofFIG. 1;

FIG. 3 is a schematic sectional view showing the configuration of anexample of a conventional surface-mount-type white LED;

FIG. 4 is a schematic sectional view showing the state of settlement offluorescent particles in the transparent resin portion of thesurface-mount-type white LED of FIG. 3;

FIG. 5 is a schematic sectional view showing another embodiment of anLED made in accordance with the principles of the invention;

FIG. 6 is a schematic sectional view showing another embodiment of anLED made in accordance with the principles of the invention; and

FIG. 7 is a schematic sectional view showing another embodiment of anLED made in accordance with the principles of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described withreference to FIGS. 1, 2 and 5-7 of the accompanying drawings. Although avariety of technical features are imparted to the following embodiments,which are merely specific examples of the present invention, the scopeof the invention is not to be construed as being limited thereto.

FIG. 1 shows a configuration of an embodiment of a white LED made inaccordance with the principles of the invention. In FIG. 1, the whiteLED generally designated at 10 can be configured as a so-calledsurface-mount-type LED and can include a chip substrate 11, a blue LEDchip 12 mounted on the chip substrate 11, and a transparent resinportion 13 having a wavelength conversion material, such as afluorescent material 13 a, mixed therein. The transparent resin portion13 can be formed on top of the chip substrate 11 in such a manner as tosubstantially surround the blue LED chip 12.

The chip substrate 11 can be formed from a heat-resistant resin such asa flat copper-clad wiring board, for example, and can include on itssurfaces a chip mount land 11 a, a connection land 11 b, and surfacemounting terminals 11 c and 11 d extending therefrom via opposite endedges to its undersurfaces. In this case, since the chip substrate 11has a reduced surface area due to the downsizing of the entire LED, thechip mount land 11 a is positioned such that it is offset toward oneside (leftward in the diagram), not at the center of the top surface ofthe chip substrate 11.

The blue LED chip 12 is of a known configuration and can be joined viadie bonding or other attachment method/structure, onto the chip mountland 11 a of the chip substrate 11. An electrode can extend from the topof the blue LED chip 12 and be electrically connected via wire bondingetc. to the adjoining connection land 11 b.

The blue LED chip 12 can be formed as a GaN chip, for example, such thatit emits light having a peak wavelength at 450 to 470 nm when a drivevoltage is applied.

The transparent resin portion 13 can be formed from a transparentmaterial, e.g., transparent epoxy resin, with fluorescent material 13 ain the form of fine particles mixed therein, and can be molded onto thechip substrate 11 before hardening. Blue light from the blue LED chip 12impinges on the transparent resin portion 13 so that the fluorescentmaterial 13 a is excited to generate yellow light known as excitationlight from the fluorescent material 13 a, thus emitting white light as aresult of the mixture of those colors of light.

The wavelength conversion material can be a fluorescent material 13 athat is capable of issuing a wide color range of light around trueyellow. The material can be a cerium-doped YAG fluorescent material,cerium-doped TAG fluorescent material, orthosilicate fluorescentmaterial (BaSrCa)SiO4, or other similar material. The fluorescentmaterial 4 a can be arranged to issue a fluorescent light having itspeak wavelength at 530 to 590 nm, for example.

Although some of the characteristics and features of the aboveconfigurations are similar to that of the conventionalsurface-mount-type white LED 1 shown in FIG. 3, the white LED 10 of FIG.1 allows the fluorescent material 13 a to be offset toward the LED chip12 within the transparent resin portion 13. In other words, thefluorescent material 13 a can be mixed at a higher density within thetransparent resin portion 13 at a location close to the LED chip 12 ascompared to a location away from the LED chip 12.

Such a distribution of density can be obtained by disposing thetransparent resin portion 13 and the chip substrate 11 such that the endof the transparent resin portion 13 closer to the LED chip 12 orientsdownward as shown in FIG. 2 when the transparent resin portion 13 ishardened.

As a result, the fluorescent material 13 a mixed in the transparentresin making up the pre-hardening transparent resin portion 13 descendsdue to gravity as indicated by arrow A in FIG. 2, based on thedifference in the specific gravity between the fluorescent material andthe transparent resin. The fluorescent material 13 a (or otherwavelength converting material), then settles down toward the LED chip12 within the transparent resin portion 13.

Accordingly, by making use of certain features of the conventionalmanufacturing process for a white LED 1, a desired distribution ofdensity of the fluorescent material 13 a can be obtained through asimple operation of altering the direction of the transparent resinportion 13 and the chip substrate 11, as shown in FIG. 2, when thetransparent resin portion 13 is being hardened. This process may notrequire additional members/structures and/or unnecessary process steps.

FIG. 5 shows another embodiment of an LED made in accordance with theprinciples of the present invention. In particular, FIG. 5 shows the LEDformed as a cannonball type LED in which the blue LED chip 12 can belocated within a lens shaped resin material portion 13. Wavelengthconversion material 13 a can be dispersed within the resin portion suchthat the density of wavelength conversion material 13 a is higheradjacent the LED chip and less dense further from the LED chip 12. Theelectrodes for the LED can be formed as two parallel extending leadframes 19 a and 19 b.

FIG. 6 shows yet another embodiment of an LED made in accordance withthe principles of the present invention. In FIG. 6 the LED is alsoformed as a cannonball type LED in which the blue LED chip 12 can belocated within a resin material portion 13. A transparent lens shapedresin portion can be formed over the LED chip 12 and resin materialportion 13. Wavelength conversion material 13 a can be dispersed withinthe resin portion 13 such that the density of the wavelength conversionmaterial 13 a is higher adjacent the LED chip and less dense furtherfrom the LED chip 12. The electrodes for the LED can be formed as twoparallel extending lead frames 19 a and 19 b.

FIG. 7 shows another embodiment of an LED made in accordance with theprinciples of the present invention. In FIG. 7 the LED includes an LEDchip 12 located within a resin portion 13. A frame member 18 can bemounted to the chip substrate and can include a recessed portion that isupwardly flared. The LED chip 12 and transparent resin portion 13 can belocated within the recessed portion of the frame member 18 such thatlight emitted by the LED chip 12 is reflected in a particular directionby the walls of the recessed portion.

The LED 10 can be thus configured, and application of a drive voltage tothe blue LED chip 12 via the surface mounting terminals 11 c and 11 d(or lead frames 19 a and 19 b) causes emission of light of the blue LEDchip 12. Part of the blue light issuing from the blue LED chip 12impinges on the fluorescent material 13 a mixed in the transparent resinportion 13 such that the fluorescent material 13 a is excited togenerate yellow light. This yellow light mixes with the blue light fromthe blue LED chip 12, resulting in white light which in turn travelsthrough the interior of the transparent resin portion 13 and is emittedto the exterior of the device.

In the above examples, the fluorescent material 13 a exists at higherdensity around the

LED chip 12 within the transparent resin portion 13, whereas the densityof the fluorescent material 13 a becomes lower in the region outside thesurroundings of the LED chip 12.

Hence, while in FIG. 1, light L outgoing from the LED chip 12 toward theother sides travels through a longer distance within the transparentresin portion 13, there is not much difference between the number offluorescent particles 13 a struck by the light L and the number offluorescent particles 13 a struck by light L′ outgoing from the LED chip12 toward one side within the transparent resin portion 13 due to thelower density of the fluorescent material 13 a in the regions far fromthe LED chip 12. This means that light from the LED chip 12 excitessubstantially the same number of fluorescent particles 13 a in alldirections, thus generating substantially the same yellow light byexcitation in all directions. Thus, light that is emitted from theentire transparent resin portion 13 of the LED 10 to the exterior indifferent directions experiences little or no unevenness in colordepending on direction, and can present a generally uniform white light.

In this manner, according to the surface-mount-type white LED 10, eventhough blue light emitted from the LED chip 12 in certain otherdirections travels through a longer distance within the transparentresin portion 13, they can impinge on substantially the same number offluorescent particles 13 a as light in other directions. This is due tothe lower density of the fluorescent material 13 a in particular areasof the resin portion 13. Therefore, light emitted from the LED chip 12in different directions mixes with yellow light presented by thefluorescent particles 13 a so that generally uniform white light can beissued without causing substantial unevenness in color with respect tovarious directions.

At that time, making use of certain features of the conventional whiteLED manufacturing process without need for additional members/structuresfor implementation or unnecessary process steps, the present LED caneasily be manufactured at low cost without additional facility costs bykeeping the transparent resin portion 13 and the chip substrate 11 in apredetermined direction during the time that the transparent resinportion 13 is hardened.

Although a so-called lamphouse is not disposed around the blue LED chip12 in the above described embodiments, use of an LED provided with alamphouse is contemplated in conjunction with the present invention.Although the blue LED chip 12 is mounted on the chip mount substrate byway of example in the above surface mount embodiment, a so-calledcannonball-type LED mounted at one extremity of two lead frames, alongwith other LED structures, for example, are contemplated for use withthe principles of the present invention.

Although, in the above described embodiments, blue light from the blueLED chip 12 is converted via fluorescent material 13 a into yellow lightto obtain white light as a result of mixture of the blue light with theyellow light, mixture or emission of other colors is also contemplatedby the present invention. For example, an LED configured in accordancewith the principles of the invention could convert light from the LEDchip into light of other color by the fluorescent material so that colormixture of the light from the LED chip and the excitation light from thefluorescent material is issued to the exterior.

Furthermore, although the above described embodiments use fluorescentmaterial for the purpose of converting the wavelength of light from theLED chip, the present invention is not intended to be limited thereto.Use of other wavelength conversion material is also contemplated by thepresent invention.

Thus, an extremely excellent LED that emits light of generally uniformcolor, even in the case where the LED chip is not positioned at or nearthe center of the chip substrate, can be obtained.

While there has been described what are at present considered to bepreferred embodiments of the present invention, it will be understoodthat various modifications may be made thereto, and it is intended thatthe appended claims cover all such modifications as fall within the truespirit and scope of the invention.

1. An LED comprising: a pair of electrode members having a chip mountportion; an LED chip located adjacent the chip mount portion and on oneof the pair of electrode members, the LED chip electrically connected tothe pair of electrode members; and a transparent resin portion withwavelength conversion material mixed therein, the transparent resinportion formed in such a manner as to substantially surround the LEDchip, wherein the LED chip is positioned such that it is offset towardone side in the transparent resin portion, and wherein the wavelengthconversion material mixed in the transparent resin portion has a higherdensity near the side that the LED chip is positioned, and a lowerdensity away from the side, within the transparent resin portion.
 2. TheLED of claim 1, further comprising a lens portion made of a transparentresin surrounding the LED chip and the transparent resin portion.
 3. TheLED of claim 1, wherein the pair of electrode members are formed on achip substrate and are in the form of electrically conductive patternsextending to an underside of the chip substrate to define surfacemounting terminals.
 4. The LED of claim 3, wherein the transparent resinportion is filled within a recessed portion that is upwardly flared soas to allow exposure of the chip mount portion in the form of aframe-shaped member formed on the chip substrate.
 5. The LED of claim 1,wherein the wavelength conversion material is dispersed within thetransparent resin portion in a density pattern governed by orienting thetransparent resin portion such that a side of the transparent resincloser to the LED chip is facing downward towards a gravitational forcewhen the transparent resin is being hardened.
 6. The LED of claim 1,wherein the wavelength conversion material increases in density withcloser to the side.
 7. The LED of claim 1, wherein the wavelengthconversion material is dispersed in the transparent resin portion suchthat light emitted from the LED chip undergoes substantially equalwavelength conversion regardless of direction of emission from the LED.8. The LED of claim 2, wherein the pair of electrode members are twolead frames extending in parallel with each other.
 9. The LED of claim1, wherein the wavelength conversion material is a fluorescent material.10. The LED of claim 1, wherein light emitted from the LED chipundergoes a substantially equal amount of wavelength conversionregardless of direction of light emission for the LED.
 11. An LEDcomprising: a pair of electrode members having a chip mount portion anda wire connection portion; an LED chip located adjacent the chip mountportion, the LED chip electrically connected to the wire connectionportion by a wire; and a transparent resin portion with wavelengthconversion material mixed therein, the transparent resin portion formedin such a manner as to substantially surround the LED chip, wherein thechip mount portion is a part of one of the pair of electrode members andis located off-center of the transparent resin portion, and the wireconnection portion is a part of the other one of the pair of electrodemembers, and wherein the wavelength conversion material mixed in thetransparent resin portion has a higher density on the chip mountportion, and a lower density on the wire connection portion, within thetransparent resin portion.
 12. The LED of claim 11, wherein the wireconnection portion is located off-center of the transparent resinportion, and on the other side of the chip mount portion.
 13. The LED ofclaim 11, wherein the wavelength conversion material mixed in thetransparent resin portion has density gradient from a side of the wireconnection portion to a side of the chip mount portion.